Preparation of anatase titanium dioxide pigment

ABSTRACT

This invention relates in general to a process for preparing a high quality titanium dioxide pigment in which the titanium dioxide is in the anatase crystal form. The process comprises hydrolyzing in a particular manner the titanium values from a titanium sulfate-ferrous sulfate solution in which the concentration of titanium is from 80 to 180 g.p.l. calculated as TiO2 and treating and calcining the hydrate so formed to produce a high grade anatase TiO2 pigment. Using the hydrolysis process of the instant invention, a high grade anatase titanium dioxide pigment may be produced from a titanium sulfate-ferrous sulfate solution without utilizing the conventional crystallization step for removing most of the iron values nor the concentration step for increasing the titanium content in the liquor to at least 200 g.p.l. TiO2.

United States Patent [72] Inventors Kenneth W. Heywood Overland; Charles R. Trampier, Jr., Webster Groves, both of Mo. [21] Appl. No. 860,016 [22] Filed Sept. 22, 1969 [45] Patented Nov. 2, 1971 [73] Assignee National Lead Company New York, N.Y.

[54] PREPARATION OF ANATASE TITANIUM DIOXIDE PIGMENT 4 Claims, No Drawings 52] U.S. Cl 23/202, 106/300 [51] Int. Cl C01g 23/04, C01g 23/06, C0lg 23/08 [50] Field of Search 23/202, 1 17; 106/300 [56] References Cited UNITED STATES PATENTS 2,817,595 12/1957 Kalinowski 23/202 X 2,999,011 9/1961 Olmsted et al. 23/202 Primary Exanziner- Edward Stern A1!orne vs-Charles F. Kaegebehn, Robert L. Lehman and Robert L. Holiday ABSTRACT: This invention relates in general to a process for preparing a high quality titanium dioxide pigment in which the titanium dioxide is in the anatase crystal form. The process comprises hydrolyzing in a particular manner the titanium values from a titanium sulfate-ferrous sulfate solution in which the concentration of titanium is from 80 to 180 g.p.l. calculated as TiO and treating and calcining the hydrate so formed to produce a high grade anatase TiO pigment. Using the hydrolysis process of the instant invention, a high grade anatase titanium dioxide pigment may be produced from a titanium sulfate-ferrous sulfate solution without utilizing the conventional crystallization step for removing most of the iron values nor the concentration step for increasing the titanium content in the liquor to at least 200 g.p.l. TiO- PREPARATION OF ANATASE TITANIUM DIOXIDE PIGMENT BACKGROUND OF THE INVENTION Titanium dioxide pigments are generally produced commercially according to the prior art processes by the so-called sulfate process in which a titaniferous material, such a titaniferous iron ore, ore concentrate or a titanium slag is heated at elevated temperatures, with concentrated sulfuric acid to form a porous cake, sometimes referred to in the art as .digestion cake." The digestion cake is allowed to cure so as to effect maximum recoveries of titanium values upon dissolving. After curing, the cake is dissolved in water or weak acid, with agitation, to form a solution of titanium sulfate and iron sulfates. The ferric sulfate values in the solution are converted to ferrous sulfate by the addition, to the solution, of a reducing agent, such as scrap iron with or without antimony oxide. The solution is then clarified by settling and filtration to remove all of the solid material contained in the solution with minimum loss of TiO,.

Following clarification the solution is then usually subjected to a crystallization step to remove most of the ferrous sulfate values as copperas, i.e., FeS '7I'l O.

After crystallization the titanium sulfate solution is subjected to concentration to remove water from the solution. This is accomplished by evaporation in concentrators which operate under vacuum and at elevated temperatures. Concentration is continued until the specific gravity of the solution is at least l.5 with a TiO, content of at least 200 grams per liter and preferably from 250-300 grams per liter.

The concentrated titanium sulfate solution is then converted by hydrolysis, from the soluble state into insoluble TioO, hydrate and in general this change is effected through dilution of the concentrated titanium sulfate-ferrous sulfate solution with H O at elevated temperatures. Thus a predetermined amount of titanium sulfate-ferrous sulfate solution having a TiO, content of at least 200 grams per liter is preheated to a temperature of at least 90 C. and added at a predetermined rate, with agitation, to clear water at substantially the same temperature and the ratio of 3-19 parts solution to one part water. During subsequent boiling, the precipitated Ti0 forms initially as colloidal particles, which subsequently floc to produce a filterable TiO hydrate containing from 30 percent to 36 percent solids.

High quality titanium dioxide pigments have been made from hydrates produced from clarified, concentrated and crystallized titanium sulfate solution. However the above described hydrolysis procedure cannot be employed to produce satisfactory hydrates when a clarified but unconcentrated and uncrystallized titanium sulfate-ferrous sulfate solution is used.

SUMMARY OF THE INVENTION A high quality titanium dioxide pigment having the crystal structure of anatase may be produced by the process of the instant invention which utilizes a novel hydrolysis procedure which employs a clarified but uncrystallized and unconcentrated titanium sulfate-ferrous sulfate solution having a titanium concentration from 80 to 180 g.p.l. TiO a FeSOJTioratio from 2.20 to 2.75 and a H SOJTiO- ratio from 1.70 to 2.30.

The process comprises the following steps:

1. provide a measured quantity of the above clarified, uncrystallized and unconcentrated titanium sulfate-ferrous sulfate solution at a temperature from 40 C. to 70 C.;

2. add water to a tank in which the initial hydrolysis will take place, the quantity of water being from 5 percent to percent of the volume of the said measured quantity of titanium solution to be hydrolyzed, said water being heated and agitated to obtain a temperature from 80 C. to 98 C.;

3. add from 1 percent to 5 percent of the total amount of said measured quantity of titanium solution to the water over a period of 60 to 120 seconds;

4. add from 10 percent to 30 percent of remainder of the said measured quantity of titanium solution into the mixture in the tank over a period from 5 to 20 minutes;

5. maintain the temperature of the mixture between 55 C. an C. during the addition period;

6. admixing the above mixture and the remainder of the titanium solution in a tank;

7. the temperature of the final mixture after all of the solutions have been added being between 50 C. and C.;

8. heating the mixture to boil within 20 to 70 minutes;

9. boil the mixture gently from 2 to 4 hours;

l0. filter and thoroughly wash the precipitated titanium hydrate;

l1. bleach the washed hydrate to reduce the ferric iron values to the ferrous state and after filtering and washing;

12. add water to form a titanium hydrate slurry;

l3. treat the slurry with salts of potassium and phosphorous in amount equivalent to 0.3-0.5 percent K 0 and 0.4-0.8 percent P205 on a Tio weight basis, the mole proportions of K OzP obeing from 0.94:3: l .0;

l4. calcine the dewatered slurry to fonn anatase TiO, having a spectral characteristic of at least 3.5 with a rutile content of less than 2 percent;

15. and milling calciner discharge to form said anatase pigment.

In the instant process, it should be noted that the nucleating agent formed in step (3) is then stabilized by the addition of 10 percent to 30 percent of the remaining titanium solution in step (4). This stabilized nucleating agent may be prepared ahead of time and used later in various hydrolysis batches since it may be stored for various-lengths of time.

In step (6) wherein the stabilized nucleating agent prepared in step (5-) is admixed with the remaining titanium solution, it should be explained that the stabilized nucleating solution and the remaining solution may be admixed in any manner. The two solutions may be simultaneously added to an empty tank, the stabilized nucleating solution may be added to the remaining solution or the latter may be added to the former. Although any method of mixing may be used, it is preferred to add the two solutions simultaneouslyor cocurrently, the stabilized nucleating solution being added over a period of l0 to 15 minutes as the remaining solution is being added over a period of 20to 40 minutes.

This particular hydrolysis process for preparing anatase titanium dioxide pigment from an unconcentrated, uncrystallized solution is particularly desirable since the seed or nucleating agent may be prepared in advance and may be stored until ready for use in a subsequent hydrolysis batch. In addition the seed or nucleating agent is prepared in situ and therefore does not require the purchase of relatively pure alkali metal compounds which normally are used to prepare outside nuclei.

If it is desirable to produce an anatase pigment having a particularly high spectral characteristic, a holding period of from 1 to 5 minutes between the end of step (3) and the beginning of step (4) is useful.

It has also been discovered that the settling and filtering characteristics may be improved if desired, if the speed of agitation is intensified in step (2) during the initial solution addition in step (3).

When using the instant hydrolysis process for hydrolyzing a clarified but uncrystallized, unconcentrated solution, the titanium hydrateformed apparently possesses the necessary crystallite and floc sizes H. V. that upon treatment and calcination the anatase TiO pigment formed possesses the superior pigment properties.

Pigment properties were determined as follows:

The tinting, strength was determined by the well-known Reynolds Tinting Strength Method as described in Physical and Chemical Examination of Paints, varnishes, Lacquers; and colors by H; V. Gardner, Ninth Edition, May 1939, page 37.

The color brightness and tone were determined by'th'e fol lowing methods:

of the titanium dioxide pigment in a wet film of alkyd vehicle. The pigment was dispersed in a soya alkyd vehicle and the tion. The temperature ofthe mixture at the end of the addition period was 80 C.

This stabilized solution was then added simultaneously with the remaining 1560 cu. ft. of titanium solution to a tank, the

5 time of addition of the stabilized solution was 1 1 minutes green red and blue reflectance values of mm were mea' while the time of addition of the remainder of the titanium sured. The green reflectance value was taken as a measure- Solution was 28 minutes ment of the brightness of the pigment and the blue minus red steam was added to h the mixture and at the end of the refleciance values as a measure of the color tone The deter' solution addition the temperature of the mixture was 82 C. minanons were made on a Colormaster Differeptial Coloring The mixture was heated to a boil in 35 minutes and was boiled manufactured by Manufacturers Engmeenng and Equlp' for 3 hours after which the precipitated hydrate was allowed ment F Hatboro 2 to settle, the liquor removed and the hydrate was washed and The pigment was mixed with a soya alkyd resin to form a thoroughly bleached to remove the iron and other coloring paste and the Paste apphed to surface of a hlgh impurities. in this particular example the iron in the hydrate reflectance white ceramic panel, the thickness of the paste was reduced to 0.003 percent Fe O which is below the upper film being sufficient to eliminate the background color. The hmhofo 005 percent Fe 0 z a green, red and blue reflectance values of the film were read on The wshed and bleaczhgd titanium hydram was then ship the Colormaster and the reflectances were recorded as pertied with water to obtain 30 percent solids. The Slurry was cent reflectance' then treated with 0.45 percent K 0 (added as 10 percent The spectral characteristic of the pigment was determined K2504 Solution) and Q65 percent P205 (added as 75 percent as follows: l-l PQ, the percentages based on the amounts retained in the SPECTRAL CHARACTERISTICS OF PIGMENT [N A hydrate and based on the weight of TiO, in the slurry. After PAINT VEHICLE agitating the treated slurry for one hour, the slurry was filtered and the treated hydrate was introduced into the calciner.

The P was mixed with a y alkyd Vehicle containing The hydrate was calcined for 100 minutes at 950 C. after carbon black and the mixml'e was formed into a P The which the calcined TiO was thoroughly milled. The milled ratio of the pigment to carbon black present in the paste was 5 i t ha the following properties: to 0.15. The paste was then spread onto a lacquered sheet and the wet film was immediately tested in the Colormas r a Reflectance 95.5 Colorimeter described above. The blue and red reflectance T n: values were obtained. The spectral characteristics of the pig- Rwnmds-nmlns 99 ment was measured by comparing the result obtained by sub- Spam! Chmcm'sw tracting the red from the blue reflectance values and compar- EXAMPLES 2 4 ing this result with the spectral characteristics of a standard pigment previously determined. The procedure of example 1 was repeated in these examples In order to describe more fully the process of the instant inexcept h the mfclel was Slablhzed Wlih Varying vention the f ll i examples arc presented; the titanium solution. In example 2, 10 percent of the remaining solution was used while 30 percent was used in example 3. EXAMPLE 1 0 In example 4 has the stabilized nucleating solution was held for 2 hours before bein used in the final hydrolysis ste in all Two hun.dl:ed of waiter l to 91 were plced of these examples the st abilized nucleating solution wafadded into a precipitation tank. With agitation 40 cu. ft. of clarified Simultaneously to a tank with the remaining solution but uncrystallized, unconcentrated titanium sulfate-ferrous The operational details and the results obtained h each of sulfate solution at 50 C. were added to the water within 90 these examples along with those of example 1 are recorded in seconds. 40 cu. ft. of the sulfate solution represents 2 percent the following table of the total amount of solution to be hydrolyzed. The solution employed has the following analysis: EXAMPLES 5-6 Specific 6mm a L530 In these examples the procedure of example 1 was used exrio, a 8.6 cept that the stabilized nucleating solution and the remaining ii,so, a) (to methyl orange] 16.5 titanium solution were not added simultaneously to the Sig 3 precipitation tank. in example 5 the stabilized nucleating solu- I tion was added the remaining titanium solution which had Red.TiO, ,.gpl. 3.0 been previously placed in the precipitation tank while in example 6 the stabilized nucleating solution was first placed in Immediately after the initial solution had been added, 400 cu. ft. of the titanium solution were added to the tank over a period of 7 minutes to stabilize the nuclei. This amount of solution represented 20 percent of the total amount of soluthe precipitation tank and the remaining titanium solution was added to the stabilized nucleating solution.

The results of these runs along with the operational details are recorded in the table.

TABLE 1 Example Number Hydrolysis 1 2 3 4 5 6 Amount of H20 Used (21.1., IL 200 200 200 200 200 200 Temp. of H20, 91 J1 Eli 91 91 Amount of solution, added ini ft 40 40 40 4O 40 40 Amount of solution, added initially percent V 2 2 L! .2 2 2 Temperature of solution, C 50 48 55 50 50 50 Time of addition, seconds 90 88 100 90 90 Amount 01 solution added, to stabilize Lli nuclei, cu. ft 400 200 600 400 400 400 Amount of solution added to stabilize the nuclei, percent .20 10 30 20 20 20 Temperature of mixture, C. 80 81 T8 80 80 80 Time of addition, min 7 5 l1 7 7 7 Method 01 admixing nucleating solution and remaining titanium solution. t Amount of remaining solution added, cu.

Table l-Continued Time of addition, minufies 28 23 24 28 28 Amount of stabilized solution added, cu.

ft 640 440 840 840 640 640 Time of addltlon, minutes. 11 7 14 ll 11 T me to heat to boil, minutes. 35 35 35 35 45 40 Time at b011, hours. 3 3 3 3 3 3 Treating agents:

K20, percent. 0. 45 0. 45 0.45 0. 45 0. 45 0. 45

2 5 0.65 0. 55 0.65 0.65 0. 65 0.65 Calcmation:

Temperature, C. 950 950 950 950 950 950 Time, minutes 100 100 100 100 100 100 Plgment properties:

Reflectance percent 95. 5 95. 5 '95. 6 D6. 95. 6 95. 6 Tone .-3.9 4.1 3.8 3.9 -3.7 -4. 1 Reynolds tintin strength- 1, 225 1,200 1, 225 1, 225 1, 225 1, 200 Spectral characteristics 4. 0 4. 0 3. 9 4. 4 4. 3

I Simultaneously. 2 Stabil zing nucleating solution added to remaining Ti. Solution. 3 Remainlng T1. solution added to stabilized nucleating solution.

We claim:

I. A process for producing a high quality titanium dioxide pigment having the crystal structure of anatase which comprises providing an uncrystallized and unconcentrated titanium sulfate-ferrous sulfate solution at temperature of 40-70 C., having a titanium concentration from 80 to I80 g.p.l. TiO,, a FeSoJTiO- ratio from 2.20 to 2.75 and a H So /TiO, ratio from 1.70 to 2.30, adding water to a tank in which the hydrolysis will take place, the quantity of water being from 5 percent to percent of the volume of the titanium solution to be hydrolyzed, heating and agitating the water to obtain a temperature from 80 C. to 98 C., adding from 1 percent to 5 percent of the total amount of said measured quantity of titanium solution to the agitated water over a period of 60 to 120 seconds to form a nucleating agent, adding from 10 percent to 30 percent of remainder of the said measured quantity of titanium solution into the mixture to stabilize the nucleating agent in the tank over a period of from 5 to minutes, maintaining the 20 of the mixture between 55 C. and 85 C. during the addition period, admixing the above stabilized nucleating mixture with the remainder of the titanium solution in a tank, the temperature of the final mixture after all of the solutions have been added being from 50 C., to 90 C., raising the temperature of the mixture to a boil within 20 minutes to 70 minutes after the end of the addition period, boiling gently the mixture from 2 to 4 hours, filtering thethoroughlywashing the precipitated titanium hydrate, bleaching the 'washed hydrate to reduce the ferric iron values to the ferrous state and after filtering and washing, adding water to form a slurry. treating the slurry with salts of potassium and phosphorous, in amount equivalent to 0.3-0.5 K 0 and 0.4-0.8 p 0 on a Ti0 weight basis, the mole proportions of x oano, being from 0.9-1.3: l .0, dewatering the slurry and calcining the dewatered slurry to form anatase TiO having a spectral characteristic of at least 3.5 with a futile content of less than 2 percent and milling the calciner discharge to form said anatase pigment.

2. Method according to claim 1 in which the stabilized nucleating agent is added simultaneously with the remaining titanium solution to a precipitation tank, the time of addition of said stabilized nucleating agent being from 10 to 15 minutes and the time of addition of the remainder of the titanium solution being from 20 to 40 minutes.

3. Method according to claim 1 in which the stabilized nucleating agent is added to the remainder of the titanium solution.

4. Method according to claim 1 in which the remainder of the titanium solution is added to the stabilized nucleating agent.

While this invention has been dacfibedandinustratedby the examples shown, it is not intended to be strictly limited thereto, and other variations and modifications may be employed within the scope of the following claims. 

2. Method according to claim 1 in which the stabilized nucleating agent is added simultaneously with the remaining titanium solution to a precipitation tank, the time of addition of said stabilized nucleating agent being from 10 to 15 minutes and the time of addition of the remainder of the titanium solution being from 20 to 40 minutes.
 3. Method according to claim 1 in which the stabilized nucleating agent is added to the remainder of the titanium solution.
 4. Method according to claim 1 in which the remainder of the titanium solution is added to the stabilized nucleating agent. 